Compared to traditional electromagnetic type motors, ultrasonic motors have various advantages, such as fast response, high precision, independence to electromagnetic interference, no complicated coil structure. Due to the linear driving characteristic of the ultrasonic linear motors, bulk and complicated screw conversion mechanism and power consumption during motion conversion can be eliminated. In addition, ultrasonic motors is self-locking when no power is applied, this saves energy when stationary, unlike the traditional electromagnetic type motors. Therefore, ultrasonic motors have gradually took over the place of electromagnetic motors and been widely used in producing micro-driving elements, such as in the driving element of a camera lens.
The driving mechanism of a typical ultrasonic linear motor uses vibrations generated on a surface of a vibrator in the motor to actuate a slider to rotate or linearly translate. Commercially available ultrasonic linear motor can generally be classified into two types: stepper type and resonant type. The former one performs stepping movement in units of a few nanometers, whereas the latter one operates under a resonant condition of the vibrator and drives the slider using resonant waves. Both have their benefits, the former one has high positioning resolution, while the latter one has high efficiency and high motion speed due to the resonant condition. Stepper type ultrasonic linear motors are mostly used for nano-scale positioning in laboratories or semiconductor manufacturing processes. On the other hand, resonant type ultrasonic linear motors are highly efficient and simple to drive, they are especially suitable for consumer electronic products, such as miniaturized (photo or video) cameras with the ability to avoid handshaking and/or enable optical zooming, or for highly secure automatic electronic locks that are immune to electromagnetic interference.
However, one problem currently encountered in designing ultrasonic linear motors is that the shapes of the ceramic vibrators cannot be easily manufactured, since ceramic is a fragile material. If the shape of the vibrator is complicated, it cannot be molded in a single run, and subsequent cutting processes can be difficult (referring to U.S. Pat. Nos. 7,105,987, 7,053,525 and 7,205,703). Furthermore, the amount of accompanying elements can be numerous (referring to U.S. Pat. Nos. 5,453,653, 6,765,335 and US Publication no. 2008/073,999, all of which require additional bearing members, or referring to U.S. Pat. No. 6,747,394, which uses two vibrators and the performance of such motor may be affected since the dynamic characteristics of these two vibrators might be slightly different), and structures are more complicated. Accordingly, assembly precision is critical for these types of motors, such that they cannot be manufactured at a low cost. Furthermore, if the fixing structure of the vibrator is not well designed, it may suppress vibrator oscillation during operation.
Thus, there is a need for an ultrasonic linear motor that has few elements, a simple structure and can be easy to manufacture and integrate with other elements, thereby reducing manufacturing cost and requirements of high assembly precision.